1. Field of the Invention
This invention relates to technology for printing an image by forming dots on a print medium.
2. Description of the Related Art
As output devices for images created using a computer or images shot using a digital camera or the like, printing devices that print images by forming dots on a print medium are widely used. These printing devices perform gradation expression using a halftone process because there are few dot tone values that can be formed for the input tone values. As one halftone process, an ordered dither method using a dither matrix is widely used. The ordered dither method has a big effect on the image quality according to the dither matrix contents, so for example as disclosed in JP-A-7-177351, JP-A-7-81190, and JP-A-10-329381, an attempt was made to optimize the dither matrix using an analysis method of simulated annealing or genetic algorithm using an evaluation function taking into consideration the human visual sense. In this kind of optimization process, threshold values can be determined in sequence by selecting threshold values which has the highest tendency for dot formation to be On in the halftone process.
However, this method of determining the storage elements in the above mentioned sequence requires computational process for evaluation for each of undetermined storage elements, which leads to the huge amount of calculation.